filesystem `paths.fhs` should not set `bin_dir`
While paths.fhs is probably based on the standard, I don't see a situation where the bin_dir
could possibly be enforced by Mailman in anyway.
when using setuptools to install Core, it would put the executables depending on it's configuration, neither of which can be controlled. But when using paths.fhs
it might try to look for master
and runner
in /sbin
which might cause it fail or crash.
I don't see any real use case of setting bin_dir
unless we can control the installation process and enforce this at install time.